[time-nuts] GPS Filter

[Mike Feher]

I used to make some interdigital filters and amplifiers in the early 80's
for MDS TV reception in the 2.3 GHz range. One can easily fabricate a low
loss narrow band filter at 1.5 GHz if need be, and as mentioned before,
antennas should be easy as well. If this really becomes an issue, I am sure
there will be a lot of solutions offered and anyone with some RF experience
will also be able to handle it themselves. Regards - Mike 

Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 office
908-902-3831 cell


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Ziggy
Sent: Friday, March 04, 2011 7:47 PM
To: time-nuts at febo.com
Subject: Re: [time-nuts] GPS Filter

The discussion got me to thinking about how we used to filter out nearby 
interference on amateur TV - namely by using interdigital filters. This 
led to a search for GPS interdigital filters which i did indeed find. 
See Alison Microwave website at 
<http://www.amlant.co.uk/DetailsAD430.htm> for one example of an 
integrated antenna/filter/preamp. (I'm sure these aren't cheap, but I 
haven't asked.) As for retrofitting, you could add a filter after the 
antenna/amplifier assembly but I might be concerned that the amplified 
GPS antenna is pretty wide and may have trouble with a Lightsquared 
transmitter nearby. There are passive antennas though, and there are 
in-line amps - you'd need to add the filter in between. We made these 
ourselves for 439 and 1296 MHz - GPS L1 isn't much above that so with 
some care it should be doable. The tuning can be finicky though :\

Ziggy

On 03/04/2011 03:31 PM, John Ackermann N8UR wrote:
> Here's a measurement we did a few years ago on the HP 58535A:
>
http://www.febo.com/pages/hp_gps_splitter/port_1_hp_58535a_two_port_amp.png 
>
>
> John
> ----
> On 3/4/2011 1:31 PM, Bob Camp wrote:
>> Hi
>>
>> Ok, now it's pretty obvious the RF world near your GPS will be 
>> changing a *lot* in the near future. Lightsquared and a bunch of 
>> similar outfits will be camping out right next door with very high 
>> power gear. They will be running 1.5KW from somewhere in town. GPS is 
>> running 30 watts from off planet.
>>
>> Has anybody tossed the various HP / Symmetricom GPS splitters on a 
>> network analyzer? If so, what do the filters in them look like?
>>
>> I probably should corner the market on these things before asking a 
>> question like that.
>>
>> The new neighbors will be at 1525 to 1559 MHz.  GPS L1 is at 1575.42 
>> MHz.  That's what we are using for timing. L2 is down at 1227.5, 
>> right now it's mainly military use. Obviously these guys are a bigger 
>> deal for civilians than the military.
>>
>> So the question is - do the built in splitter filters have any real 
>> rejection 15 to 50 MHz off of center?
>>
>> Probably worth checking. It would be a pleasant surprise if they 
>> turned out to be useful.
>>
>> Bob
>>
>>
>>
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